A high power diffused metal oxide semiconductor (DMOS) transistor typically has a threshold voltage of about 2-3 volts. Such devices are often employed as switches or control elements. In what is called a high-side driver application the power transistor drain is connected to the power supply line and the source, which provides the output potential, is brought to a potential level very close to that of the power supply. To do so requires that the gate must be driven above the power supply voltage by well over a threshold voltage. It has been found that an output driver N channel DMOS transistor requires a gate overdrive of 5 to 10 volts. When one considers that a commonly used supply voltage is 5 volts, it can be seen that the gate drive should be a multiple thereof.
The invention is intended for use in connection with complementary metal oxide semiconductor (CMOS) structures. Here N-channel and P-channel MOS transistors are combined on a common silicon substrate. In the so-called P-well construction an N-type common substrate has P-channel transistors created therein. P-type wells diffused into the substrate are employed to contain the N-channel transistors.
Alternatively, a P-type substrate can contain the N-channel transistors and N-type wells are diffused therein. The N-wells then contain P-channel transistors. In either case, the transistors contained in the wells are isolated from the others by virtue of the well-to-substrate junction.